I love using Jazz harmony. One of my favorites is tritone subs on ii-V-I progressions to get a chromatic bass line at the cadence.
EX in C:
Instead of the usual Dmin7, G7, Cmaj7...
Dmin, Db7, Cmaj7
When I get to a dominant seven chord, I also like to add some extra notes for color. So if I'm in C and my V7chord is G7, I might voice a crazy chord like this (going up): G D F G# B E
So it's basically the equivalent of a G7 with an Emaj on top. Or something like that.
I also like doing jazzy stuff like constant modal interchange. I also like to add the #4 (lydian) on a lot of Maj7 chords.
I just started getting into jazz harmony recently and it is opening up a whole new world of ideas.